Recent advances in the ultrasound-assisted osmotic dehydration of agricultural products: A review

Osmotic dehydration (OD) is an easy method for removing water from fruits and vegetables pieces. The combination of the sonication process (using ultrasonic sound waves) with the OD technique commonly named ultrasound-assisted OD (UAOD), can further improve the dehydration process efficiencies by increasing the mass transfer rates and enhancing final product quality. This manuscript reviews the application and impact of different UAOD conditions on the dehydration performance, and quality of dehydrated fruits and vegetables pieces. The physicochemical characteristics, mass transfer rates (moisture loss and soluble solids gain), and effective diffusivity coefficients during the UAOD treatment of fruit and vegetable pieces are considerably affected by pre-treatment techniques, sonication intensity (power or amplitude or frequency), direct or indirect sonication conditions, treatment temperature and time, osmotic solution concentration, osmotic agent (sucrose, glucose, fructose, sorbitol, trehalose, or NaCl), and structure and thickness of samples. The UAOD treatment increased the amount of weight reduction, moisture loss, and soluble solids gain. Also, this method is easy to carry out, and it can be used to shorten the processing time before various drying techniques, resulting in even higher total efficiencies of the different processes, and it has a positive influence on minimizing energy cost. The dried fruits and vegetables slices pre-treated with the UAOD have the higher antioxidant activity, higher total carotenoid content and anthocyanin compounds, higher porosity and rehydration capacity, lower shrinkage and their colour are brighter. The hyperspectral imaging technique can be useful for estimating mass transfer rates, water content, soluble solids content, shrinkage, total carotenoids, and colour indexes of fruits and vegetables products during the UAOD process.